1. Field of the Invention
The present invention relates to a determination of the type of a disc, and more particularly, to a method of quickly determining the type of a recordable/reproducible optical disc having different track pitches and an apparatus thereof.
2. Description of the Related Art
As different optical discs become available, the types of discs corresponding to an optical disc system for recording/reproducing the discs increases. The time required to recognize the type of disc loaded in the optical disc system is a factor used to evaluate performance of the optical disc system.
FIGS. 1A-1C show a conventional method of determining the type of an optical disc. In FIGS. 1A-1C, a focus error signal (FES) and a sum signal of a photodiode (PD) are detected while moving an objective lens up and down according to a type of disc, such as a high density disc, a low density disc, and a multilayer disc. That is, when a disc is loaded in an optical disc system capable of recording/reproducing both high and low density discs, the objective lens is moved up and down to detect FES and a sum signal of PD. For the high density disc, as shown in FIG. 1A, a small sum signal 104 of the PD is shown with respect to the FES 102. For the low density disc, as shown in FIG. 1B, a large sum signal 114 of PD is shown with respect to FES 112. For the multilayer disc, as shown in FIG. 1C, as many FESs 124 as the number of layers are generated. Thus, by using these two signals, the type of disc loaded in the optical disc system can be detected, whether the disc is a high density disc, a low density disc, or a multilayer disc.
In order to record/reproduce optical discs of different types, the optical disc system includes an objective lens that is capable of recording/reproducing a low density disc and a high density disc. An additional means, such as a hologram LCD or a ring shielding may be provided to the objective lens to reduce optical aberration.
Determining the type of a disc loaded in the above described optical disc system, such as a disc having a wide track pitch and a disc having a narrow track pitch, is not easy. Using a difference in the amplitude of track error signals generated due to a difference in the track pitch is one way to determine the type of a disc. However, in a conventional optical disc system, to determine whether a disc loaded in the optical disc system is a disc having a wide track pitch or a disc having a narrow track pitch, an objective lens, constituting a pickup unit, is moved up and/or down and track error signals detected after a focus control starts are referred to in determining the disc type. Therefore, it takes a long time to detect the disc type.